Emergency responders have to prepare for many different disaster scenarios. But when that involves what amounts to an unthinkable catastrophe, planning often falls short. Such shortcomings are not necessarily the fault of disaster professionals, however. Sometimes we simply do not have the means to accurately predict how a disaster will unfold.

This is certainly the case in planning for the possibility of a nuclear weapon detonated in a metropolitan area. Obvious key questions include how large an area might be affected and where first responders should go first.

According to physicist Fernando Grinstein, we have some initial understanding to address such questions, but fundamental issues remain unresolved. The reason is that existing computer models are sadly lacking. "The predictive capabilities of today's state-of-the-art models in urban areas need to be improved, validated and tested," said Grinstein in a statement issued today. "Work in this area has been limited primarily because of lack of consistent funding."

The good news is that progress is now being made on this challenging topic. At the upcoming 62nd Annual Meeting of the American Physical Society's (APS) Division of Fluid Dynamics in Minneapolis, Adam Wachtor -- a student who worked with Grinstein at the Los Alamos National Laboratory in New Mexico -- will present his efforts to improve the way that models track the movement of radioactive fall-out carried by the wind. His wind models track the aftermath of a plume of hot gas released by a small, one-ton device in a typical urban setting at a three-meter resolution.

Current models use wind direction and wind speed to draw a predicted cone-shape area of fall-out. Wachtor's results show that these models are too simple in some ways. For instance, they do not include the complex dynamics of wind movements around buildings, which can concentrate fall-out preferentially in certain areas. They also indicate that small changes in the location of the blast and the temperature of the plume released can have a large effect on the contamination patterns.

The simulation is part of a larger coordinated effort between DHS (FEMA), the National Laboratories, DTRA, NRL, and private contractors, each of which has concentrated on a different piece of the project. Other studies have shown that, depending on the situation, buildings can provide some degree of shielding from the radiation.

The hope of the researchers collaborating in this effort is to eventually provide practical information to guide first responders. "We're preparing for [a possible] crisis," says Grinstein -- however unthinkable it may be.